A Two-Step Variable-Speed Control Moment Gyroscope Control Strategy for 3U Nanosatellite Attitude Maneuvers

Agile attitude control of nanosatellites is increasingly required for high-resolution imaging, yet actuators that provide agility on larger spacecraft do not scale down well: reaction wheels are torque-limited and slew slowly, while miniaturized control moment gyroscopes (CMGs) deliver high torque but their stored wheel momentum produces a gyroscopic coupling torque that degrades fine pointing—an inherent agility–precision trade-off on low-inertia 3U platforms. This paper presents a two-step variable-speed CMG (VSCMG) strategy that preemptively decelerates the wheel momentum once the attitude error falls below a threshold, attenuating the gyroscopic torque before fine pointing and thus decoupling slewing from precision pointing. It is validated on an experimentally grounded model: a fabricated 1U-class four-CMG pyramid (90×90×105 mm, 584 g), gimbal dynamics identified experimentally (93.2% fit) and regulated by an integral-type optimal servo, and bench-measured wheel dynamics. At 560 km under aerodynamic and gravity-gradient disturbances, the strategy completes a 90° slew in 25.3 s at a mean slew rate of 3.55°/s with 0.42° accuracy—4.5× faster than a reaction-wheel system and 12× more accurate than single-mode CMG operation—with a Lyapunov-based stability guarantee. The spacecraft-level closed-loop performance is established in closed-loop simulation, while the component-level ground experiments verify only that the assumed wheel-speed and gimbal-rate envelopes are achievable on the prototype; the present work is thus a simulation study supported by experimentally identified actuator models, not a system-level experimental demonstration. These results show that momentum-managed VSCMG control substantially relieves the agility–precision trade-off within a 1U envelope under the single-axis 90° slew studied here, extending CMG-class agility to small form-factor satellites previously confined to reaction wheels.